1. Field of the Invention
This disclosure is directed to nanocrystal-metal oxide-polymer composites and a method for preparing the composites. More specifically, each of the nanocrystal-metal oxide-polymer composites comprise a number of nanocrystals within a metal oxide matrix, and an oligomer or polymer covalently bonded to organic reactive groups of the metal oxide matrix to achieve improved stability.
2. Description of the Related Art
A nanocrystal is a crystalline material having a size of a few nanometers and consists of several hundred to several thousand atoms. Since a nanocrystal has a large surface area per unit volume, most of the constituent atoms of the nanocrystal are present at the surface of the nanocrystal and unexpected characteristics (e.g., quantum confinement effects) of the nanocrystal are exhibited. These structural characteristics account for unique electrical, magnetic, optical, chemical and mechanical properties of nanocrystals different from those inherent to the constituent materials of the nanocrystals.
The luminescent properties and electrical properties of nanocrystals can be controlled by manipulating various factors, such as size and composition, of the nanocrystals. Therefore, nanocrystals can find application in various industrial fields, including but not limited to light-emitting devices (e.g., light-emitting diodes (“LEDs”), electroluminescent (“EL”) devices, laser devices, holographic devices and sensors) and electrical devices (e.g., solar cells and photodetectors).
A wet-chemical process is typically used to produce nanocrystals. According to this process, a precursor material is added to an organic solvent capable of being coordinated to the precursor material and is grown into nanocrystals having various sizes. The precursor, a dispersant and the solvent used for the production of the nanocrystals contain various kinds of organic materials, which remain on the surface of the nanocrystals. The introduction of functional groups into the organic materials enables the nanocrystals to be stably present in solvent systems having different polarities. This stability makes the nanocrystals suitable for use in a wider variety of technological applications, including but not limited to bio-applications. Further, an advantage of the nanocrystals in the form of composites is that high reliability can be ensured irrespective of ambient conditions.
However, a solid-state device employing nanocrystals may suffer from serious instability and decomposition due to the presence of organic materials. A surfactant and a solvent used for the production of the nanocrystals by wet synthesis and a dispersant, a precursor and another surfactant used for the preparation of nanocrystal composites may be freely exposed without being completely bound and fixed to the nanocrystals and a metal oxide to cause problems in terms of performance and stability of the device.